Distributed Linear Convolutional Space-Time Coding for Two-Relay Full-Duplex Asynchronous Cooperative Networks

In this paper, a two-relay full-duplex asynchronous cooperative network with the amplify-and-forward (AF) protocol is considered. We propose two distributed space-time coding schemes for the cases with and without cross-talks, respectively. In the first case, each relay can receive the signal sent by the other through the cross-talk link. We first study the feasibility of cross-talk cancellation in this network and show that the cross-talk interference cannot be removed well. For this reason, we design space-time codes by utilizing the cross-talk signals instead of removing them. In the other case, the self-coding is realized individually through the loop channel at each relay node and the signals from the two relay nodes form a space-time code. The achievable cooperative diversity of both cases is investigated and the conditions to achieve full cooperative diversity are presented. Simulation results verify the theoretical analysis.Comment: 11 pages, 7 figures, accepted by IEEE transactions on wireless communication

Distributed Binary Detection over Fading Channels: Cooperative and Parallel Architectures

This paper considers the problem of binary distributed detection of a known signal in correlated Gaussian sensing noise in a wireless sensor network, where the sensors are restricted to use likelihood ratio test (LRT), and communicate with the fusion center (FC) over bandwidth-constrained channels that are subject to fading and noise. To mitigate the deteriorating effect of fading encountered in the conventional parallel fusion architecture, in which the sensors directly communicate with the FC, we propose new fusion architectures that enhance the detection performance, via harvesting cooperative gain (so-called decision diversity gain). In particular, we propose: (i) cooperative fusion architecture with Alamouti's space-time coding (STC) scheme at sensors, (ii) cooperative fusion architecture with signal fusion at sensors, and (iii) parallel fusion architecture with local threshold changing at sensors. For these schemes, we derive the LRT and majority fusion rules at the FC, and provide upper bounds on the average error probabilities for homogeneous sensors, subject to uncorrelated Gaussian sensing noise, in terms of signal-to-noise ratio (SNR) of communication and sensing channels. Our simulation results indicate that, when the FC employs the LRT rule, unless for low communication SNR and moderate/high sensing SNR, performance improvement is feasible with the new fusion architectures. When the FC utilizes the majority rule, such improvement is possible, unless for high sensing SNR

Comprehensive performance analysis of fully cooperative communication in WBANs

© 2013 IEEE. While relay-based cooperative networks (widely known in the literature as cooperative communication), where relays only forward signals from the sources to the destination, have been extensively researched, fully cooperative systems have not been thoroughly examined. Unlike relay networks, in a fully cooperative network, each node acts as both a source node sending its own data and a relay forwarding its partner's data to the destination. Mutual cooperation between neighboring nodes is believed to improve the overall system error performance, especially when space-time codes are incorporated. However, a comprehensive performance analysis of space-time-coded fully cooperative communication from all three perspectives, namel,y error performance, outage probability, and energy efficiency, is still missing. Answers to the commonly asked questions of whether, in what conditions, and to what extent the space-time-coded fully cooperative communication is better than direct transmission are still unknown. Motivated by this fact and inspired by the increasing popularity of healthcare applications in wireless body area networks (WBANs), this paper derives for the first time a comprehensive performance analysis of a decode-and-forward space-time coded fully cooperative communication network in Rayleigh and Rician fading channels in either identically or non-identically distributed fading scenario. Numerical analysis of error performance, outage probability, and energy efficiency, validated by simulations, show that fully cooperative communication is better than direct transmission from all three aspects in many cases, especially at a low-power and low signal-to-noise ratio regime, which is a typical working condition in WBANs

Signal space cooperative communication with partial relay selection.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.Exploiting the available diversity from various sources in wireless networks is an easy way to improve performance at the expense of additional hardware, space, complexity and/or bandwidth. Signal space diversity (SSD) and cooperative communication are two promising techniques that exploit the available signal space and space diversity respectively. This study first presents symbol error rate (SER) analysis of an SSD system containing a single transmit antenna and N receive antennas with maximal-ratio combining (MRC) reception; thereafter it presents a simplified maximum-likelihood (ML) detection scheme for SSD systems, and finally presents the incorporation of SSD into a distributed switch and stay combining with partial relay selection (DSSC-PRS) system. Performance analysis of an SSD system containing a single transmit antenna and multiple receive antennas with MRC reception has been presented previously in the literature using the nearest neighbour (NN) approximation to the union bound, however results were not presented in closed form. Hence, closed form expressions are presented in this work. A new lower bound for the SER of an SSD system is also presented which is simpler to evaluate than the union bound/NN approximation and also simpler to use with other systems. The new lower bound is based on the minimum Euclidean distance of a rotated constellation and is termed the minimum distance lower bound (MDLB); it is also presented here in closed form. The presented bounds have been validated with simulation and found to be tight under certain conditions. The SSD scheme offers error performance and diversity benefits with the only penalty being an increase in detector complexity. Detection is performed in the ML sense and conventionally, all points in an M-ary quadrature amplitude modulation (M-QAM) constellation are searched to find the transmitted symbol. Hence, a simplified detection scheme is proposed that only searches m symbols from M after performing initial signal conditioning. The simplified detection scheme is able to provide SER performance close to that of optimal ML detection in systems with multiple receive antennas. Cooperative communication systems can benefit from the error performance and diversity gains of the spectrally efficient SSD scheme since it requires no additional hardware, bandwidth or transmit power. Integrating SSD into a DSSC-PRS system has shown an improvement of approximately 5dB at an SER of 10-4 with a slight decrease in spectral efficiency at low SNR. Analysis has been performed using the newly derived MDLB and confirmed with simulation

End-to-End Joint Antenna Selection Strategy and Distributed Compress and Forward Strategy for Relay Channels

Multi-hop relay channels use multiple relay stages, each with multiple relay nodes, to facilitate communication between a source and destination. Previously, distributed space-time codes were proposed to maximize the achievable diversity-multiplexing tradeoff, however, they fail to achieve all the points of the optimal diversity-multiplexing tradeoff. In the presence of a low-rate feedback link from the destination to each relay stage and the source, this paper proposes an end-to-end antenna selection (EEAS) strategy as an alternative to distributed space-time codes. The EEAS strategy uses a subset of antennas of each relay stage for transmission of the source signal to the destination with amplify and forwarding at each relay stage. The subsets are chosen such that they maximize the end-to-end mutual information at the destination. The EEAS strategy achieves the corner points of the optimal diversity-multiplexing tradeoff (corresponding to maximum diversity gain and maximum multiplexing gain) and achieves better diversity gain at intermediate values of multiplexing gain, versus the best known distributed space-time coding strategies. A distributed compress and forward (CF) strategy is also proposed to achieve all points of the optimal diversity-multiplexing tradeoff for a two-hop relay channel with multiple relay nodes.Comment: Accepted for publication in the special issue on cooperative communication in the Eurasip Journal on Wireless Communication and Networkin

Asymptotically optimal cooperative wireless networks with reduced signaling complexity

This paper considers an orthogonal amplify-and-forward (OAF) protocol for cooperative relay communication over Rayleigh-fading channels in which the intermediate relays are permitted to linearly transform the received signal and where the source and relays transmit for equal time durations. The diversity-multiplexing gain (D-MG) tradeoff of the equivalent space-time channel associated to this protocol is determined and a cyclic-division-algebra-based D-MG optimal code constructed. The transmission or signaling alphabet of this code is the union of the QAM constellation and a rotated version of QAM. The size of this signaling alphabet is small in comparison with prior D-MG optimal constructions in the literature and is independent of the number of participating nodes in the network

Band Limited Signals Observed Over Finite Spatial and Temporal Windows: An Upper Bound to Signal Degrees of Freedom

The study of degrees of freedom of signals observed within spatially diverse broadband multipath fields is an area of ongoing investigation and has a wide range of applications, including characterising broadband MIMO and cooperative networks. However, a fundamental question arises: given a size limitation on the observation region, what is the upper bound on the degrees of freedom of signals observed within a broadband multipath field over a finite time window? In order to address this question, we characterize the multipath field as a sum of a finite number of orthogonal waveforms or spatial modes. We show that (i) the "effective observation time" is independent of spatial modes and different from actual observation time, (ii) in wideband transmission regimes, the "effective bandwidth" is spatial mode dependent and varies from the given frequency bandwidth. These findings clearly indicate the strong coupling between space and time as well as space and frequency in spatially diverse wideband multipath fields. As a result, signal degrees of freedom does not agree with the well-established degrees of freedom result as a product of spatial degrees of freedom and time-frequency degrees of freedom. Instead, analogous to Shannon's communication model where signals are encoded in only one spatial mode, the available signal degrees of freedom in spatially diverse wideband multipath fields is the time-bandwidth product result extended from one spatial mode to finite modes. We also show that the degrees of freedom is affected by the acceptable signal to noise ratio (SNR) in each spatial mode.Comment: Submitted to IEEE Transactions on Signal Processin

Performance Analysis of Improved Technique for Optimal Frequency Spectrum Utilization Considering Energy and Eigenvalue Detectors

Recently, exponential rise in the demand of wireless communication has led to gross reduction in the availability of wireless frequency spectrum to meet the proliferation of demands. Overlay and underlay cognitive radio used to address this problem is characterized with poor management of the assigned spectrum. The basic and essential mechanism of cognitive Radio (CR) to find unused spectrum is called Spectrum Sensing. This is important in optimizing frequency allocation for the increasing wireless communication system. Hence, this paper developed an energy efficient spectrum sensing technique for detection of white and brown space using energy and eigenvalue detector. Based on a predefined switching algorithm, the developed spectrum sensing system switches between overlay and underlay approach when there is presence of white space and brown space respectively. During the underlay approach, the cognitive user (CU) signal is coded using a Code Division Multiple Access (CDMA) to prevent primary users (PU) receiver from hearing CU signal and thereby improve the security of CU. Also, Hybrid Decode Amplify and Forward (H-DAF) cooperative relay technique is incorporated to enhance the coverage area of the cognitive user. However, during the overlay approach, H-DAF cooperative relay technique will be in sleep mode since CU can transmit with the maximum transmitting power. During the underlay approach, the received signal at the relay node is decoded, amplified, and coded using CDMA before forwarding to the CU receiver. The paper compared the performance of the two detectors by simulating the developed algorithm using MATLAB R2021a. Evaluation was based on Throughput, Spectrum Utilization Efficiency, and Spectral Efficiency by comparing Energy detector and Eigen Value detector. Keywords: Energy Detector (ED), Eigenvalue Detector (EVD), White Space, Brown Space, Spectrum Sensing (SS), Code Division Multiple Access (CDMA). DOI: 10.7176/ISDE/13-2-04 Publication date:July 31st 202

Joint space time block code and modulation classification for MIMO systems

Non-cooperative identification of unknown communication signals is a popular research area with widespread civilian and military applications. Multiple input multiple output (MIMO) systems employing multi-antenna transmission pose new challenges to signal identification systems, such as the classification of the employed space time block code (STBC) and modulation in the presence of the self-interference inherent to the multi-antenna transmission. In the existing literature, these two classification problems have been handled separately, despite the fact that they are interrelated. This letter presents a novel approach to MIMO signal identification by considering the modulation type and the STBC classification tasks as a joint classification problem